I don't know if anyone else has gotten this yet, or is planning on getting it some time soon, but take this as a word of caution, at least if you own the game on the 360. I am not sure whether the following issues go for the PC version as well.
 
The Ranger Pack DLC came out today, which adds some difficulty modes, two new weapons (well, only one of them is totally new),  and 9 new achievements for a total of 240G (why they left out the other 10G I do not know). I downloaded it, booted the game up. and started a new game in Ranger Hardcore The first problem with the DLC I noticed is that the new achievements do not show up unless you do "Compare Games" with another player. Looking at your standard achievement list will not make them appear. At least I know that Live has them in the system, but I have no idea whether they will actually unlock or not. 
 
The second and much bigger issue I noticed is with the game itself. Right from the beginning, the inventory is pretty screwed up. Bringing up your watch to check your air-filter time will also bring up your inventory, while the standard method to raise the inventory doesn't work at all. This means that I could not switch weapons at all. The only thing that worked was using Y to switch to my knife. Apparently bringing up the journal may also bring up the inventory, but I did not try that out. 
 
These problems may not go for everyone, since some people's games seem to be working fine, but if anyone is planning on getting the DLC, be warned that it may render your games with the new modes practically unplayable until it is fixed, which I seriously hope happens soon. I'm pretty surprised that such a simple update to the game's rules that has been planned for months now could turn out this broken.